Microzooplankton is heterotrophic planktons in the size range of 0~200 mm. They graze on the phytoplankton primary production and bacteria production. At the same time, they are food items of planktonic copepods. Role of microzooplankton in marine pelagic ecosystem is (1) the magnitude of energy transferred from microzooplankton to copepods and (2) the contribution of microzooplankton to the food item (microzooplankton and phytoplankton) of copepods. The energy transfer efficiencies between every trophic level (primary production-microzooplankton, bacterial secondary productionmicrozooplankton, microzooplankton growth efficiency, microzooplankton-mesozooplankton) should be studied. This paper reviewed the status of above mentioned energy transfer efficiencies in order to provide references to microzooplankton studies in China. About 60%～75% of Phyplankton primary production is grazed by microzooplankton per day. This value is significantly larger than grazing pressure by copepods (10% d^-1). The secondary production of marine planktonic bacteria equals 30% of primary production. About 80%～180% of the bacteria production was grazed by microzooplankton. The gross growth efficiency (GGE) of microzooplankton is 30%～40%. Therefore, microzoopolankton production is 21%～34% of the primary production. Copepods grazing pressure on microzooplankton production is 2%～51% per day (north coastal Spain). Thus, energy flow from microbial food web to copepod should be 0.4%～17% of the primary production, which is in the same level with the contribution of primary production. If the contribution of detritus was not considered, microzooplankton contributed more than 20% (some times as high as 50%) of the copepod food ingestion. Marine planktonic food web is a complex system. More studies are needed to elucidate every details of the production and transfer efficiency of every trophic level and, in the case of microzooplankton, of every group.